Tyrosinemia type II is an

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

condition with onset between ages 2 and 4 years, when painful circumscribed

callus A callus (: calluses) is an area of thickened and sometimes hardened skin that forms as a response to repeated friction, pressure, or other irritation. Since repeated contact is required, calluses are most often found on the feet and hands, b ...

es develop on the

pressure point Pressure points derive from the supposed meridian points in Traditional Chinese Medicine, Indian Ayurveda and Siddha medicine, and martial arts. They refer to areas on the human body that may produce significant pain or other effects when mani ...

s of the palm of the hand and sole of the foot.

Presentation

Palmar hyperkeratosis, Plantar Hyperkeratosis, hyperhidrosis, corneal opacity, corneal ulcers.

Pathophysiology

Type II tyrosinemia is caused by a deficiency of the enzyme

tyrosine aminotransferase Tyrosine aminotransferase (or tyrosine transaminase) is an enzyme present in the liver and catalyzes the conversion of tyrosine to 4-hydroxyphenylpyruvate. L-tyrosine + 2-oxoglutarate \rightleftharpoons 4-hydroxyphenylpyruvate + L-glutama ...

(), encoded by the gene ''TAT''. Tyrosine aminotransferase is the first in a series of five

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

s that converts tyrosine to smaller molecules, which are excreted by the

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

s or used in reactions that produce energy. This form of the disorder can affect the

eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

, and mental development. Symptoms often begin in early childhood and include excessive

tearing Tearing is the act of breaking apart a material by force, without the aid of a cutting tool. A tear in a piece of paper, fabric, or some other similar object may be the result of the intentional effort with one's bare hands, or be accidental. ...

, abnormal sensitivity to light (

photophobia Photophobia is a medical symptom of abnormal intolerance to visual perception of light. As a medical symptom, photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence o ...

), eye pain and redness, and painful

skin lesions A skin condition, also known as cutaneous condition, is any medical condition that affects the integumentary system—the organ system that encloses the body and includes skin, nails, and related muscle and glands. The major function of this sys ...

on the palms and soles. About half of individuals with type II tyrosinemia are also mentally disabled. Type II tyrosinemia occurs in fewer than 1 in 250,000 individuals. Inborn errors of metabolism of phenylalanine and tyrosine

Inborn errors of metabolism of phenylalanine and tyrosine

Diagnosis

Diagnosis is made based on elevated plasma tyrosine level with skin or eye lesions.

Treatment

Dietary restrictions of phenylalanine and tyrosine.

References

External links